Method and apparatus for a flash memory device comprising a source local interconnect

ABSTRACT

A method for forming a flash memory device having a local interconnect connecting source regions of a plurality of transistors within a sector allows for a highly selective wet etch of a dielectric region overlying the source region. An embodiment of the method comprises the use of an etch-resistant layer covering various features such as any gate oxide remaining over the source region, spacers along sidewalls of the transistor stacks, and a capping layer of the transistor. An in-process semiconductor device resulting from the inventive method is also disclosed.

This is a continuation of U.S. Ser. No. 11/105,834 filed Apr. 14, 2005and issued May 30, 2006 as U.S. Pat. No. 7,053,444, which was acontinuation of U.S. Ser. No. 10/668,944 filed Sep. 22, 2003 and issuedApr. 19, 2005 as U.S. Pat. No. 6,882,003, which was a division of U.S.Ser. No. 10/232,221 filed Aug. 29, 2002 and issued Sep. 23, 2003 as U.S.Pat. No. 6,624,024.

FIELD OF THE INVENTION

This invention relates to the field of semiconductor manufacture and,more particularly, to a method and structure for a source localinterconnect for a flash memory device.

BACKGROUND OF THE INVENTION

Floating gate memory devices such as flash memories include an array ofelectrically programmable and electrically erasable memory cells.Typically, each memory cell comprises a single n-channel metal oxidesemiconductor (NMOS) transistor including a floating gate interposedbetween a control (input) gate and a channel. A layer of high-qualitytunnel oxide used as gate oxide separates the transistor channel and thefloating gate, and an oxide-nitride-oxide (ONO) dielectric stackseparates the floating gate from the control gate. The ONO stacktypically comprises a layer of silicon nitride (Si₃N₄) interposedbetween underlying and overlying layers of silicon dioxide (SiO₂). Theunderlying layer of SiO₂ is typically grown on the first dopedpolycrystalline silicon (polysilicon) layer. The nitride layer isdeposited over the underlying oxide layer, and the overlying oxide layercan be either grown or deposited on the nitride layer. The ONO layermaximizes the capacitive coupling between the floating gate and thecontrol gate and minimizes the leakage of current.

To program a flash cell, the drain region and the control gate areraised to predetermined potentials above a potential applied to thesource region. For example 12, volts are applied to the control gate,0.0 volts are applied to the source, and 6.0 volts are applied to thedrain. These voltages produce “hot electrons” which are accelerated fromthe substrate across the gate oxide layer to the floating gate. Variousschemes are used to erase a flash cell. For example, a high positivepotential such as 12 volts is applied to the source region, the controlgate is grounded, and the drain is allowed to float. More common erasebias conditions include: a “negative gate erase” in which −10V isapplied to the control gate (V_(g)), 6V is applied to the source(V_(s)), a potential of 0V is applied to the body (V_(body)), and thedrain is allowed to float (V_(d)); and a “channel erase” which comprisesa V_(g) of −9V, a V_(body) of 9V, and a V_(s) and V_(d) of 9V orfloating. In each case these voltages are applied for a timed period,and the longer the period the more the cell becomes erased. A strongelectric field develops between the floating gate and the source region,and negative charge is extracted from the floating gate across thetunnel oxide to the source region, for example by Fowler-Nordheimtunneling.

In a flash memory device, the sources associated with each transistorwithin a sector are tied together, typically through the use ofconductive doping of the wafer to connect the sources of each transistorwithin a column. The columns within the sector are tied together usingconductive plugs and a conductive line.

FIG. 1 depicts a cross section of a transistor and other structures of aconventional flash electrically erasable programmable read-only memory(E²PROM) device. FIG. 1 depicts the following structures: semiconductorsubstrate assembly comprising a semiconductor wafer 10, transistorsource 12 and drain 14 diffusion regions within semiconductor wafer 10,gate (tunnel) oxide 16, floating gates 18 typically comprising a firstpolysilicon layer, capacitor dielectric 20 typically comprising anoxide-nitride-oxide (ONO) stack, control gate (word line) 22 typicallycomprising a second polysilicon layer, a transistor stack capping layer24 typically comprising silicon nitride (Si₃N₄) or tetraethylorthosilicate (TEOS), oxide or nitride spacers 26, a planar dielectriclayer 28 such as borophosphosilicate glass (BPSG), digit line plugs 30connected to drain regions 14, and a conductive line 32 typicallycomprising aluminum which electrically couples each plug 30 within a rowof transistors.

A goal of design engineers is to increase the density of the transistorsto enable a decrease in the size of the semiconductor device. One waythis can be accomplished is to decrease the size of the transistors. Asa semiconductor die typically comprises transistors numbering in themillions, even a small decrease in the transistor size can result in amarked improvement in device density. One obstacle to decreasing thetransistor size is that if the cross-sectional area of the source region12 becomes too small the electrical resistance of the source diffusionregion increases beyond a desirable level and the device may becomeunreliable. The undesirable increase in resistance is exacerbated by therelatively extreme length of the diffusion region which functions as asource region for all transistors within a column. Thus, to minimize theresistance the source region must be heavily doped with conductiveatoms. One problem with providing a heavily doped source region is thatthe dopants tend to diffuse away from the source region, especially withhigh-temperature processing of subsequent manufacturing steps. Thedopants can migrate into the channel region of the device therebyeffectively decreasing the channel length interposed between the sourceand drain regions underneath the transistor stack. This decrease inchannel length can produce problems known as “short channel effects”such as a transistor with a lowered threshold voltage, which itself canproduce an unreliable device.

One method for allowing a decrease in transistor size by decreasing thesource length which avoids short channel effects is to provide a sourcelocal interconnect (LI) 34 as depicted in FIG. 2. A source LI cancomprise the use of a conductive interconnect which electrically coupleseach source in one column of transistors of a flash device with allother sources. The interconnect is typically formed from a single layerof patterned, conductively doped polysilicon, a metal such as tungsten,or another conductive material lying between two adjacent columns oftransistors. An LI of polysilicon and a method for forming the LI hasbeen proposed by R. Lee in U.S. Pat. Nos. 5,149,665 and 5,270,240, eachof which is assigned to Micron Technology, Inc. and incorporated hereinby reference as if set forth in their entirety.

One concern with source local interconnects is to maintain an adequateisolation between the interconnect and the word lines (control gates) ofeach adjacent transistor to prevent shorting and to sustain the maximumvoltage between the source and control gate of the flash device. Forexample, in program (write) mode, 12 volts can be applied to the controlgate while 0 volts is applied to the source. While maintaining isolationis necessary, an attempt is made to keep the spacing between the LI andthe word lines to a minimum so that the transistors, and thus the memoryarray, can be made as small as possible.

A method for forming a local interconnect for a semiconductor device,and an inventive structure resulting from the method, which reduces oreliminates the problems described above would be desirable.

SUMMARY OF THE INVENTION

The present invention provides a new method for forming a semiconductordevice, and an inventive semiconductor device resulting from the method,which, among other advantages, allows for a more scaleable device thanis found with flash memory devices having diffused sources. Theinventive method and device further allows for minimal spacing between alocal interconnect and adjacent transistor features.

In accordance with one embodiment of the invention a plurality oftransistor stacks each having an associated source and drain region, anitride capping layer, and nitride spacers formed along each stack isprovided. During the etch of the transistor stacks the gate oxide istypically not completely removed from the source and drain regions andremains until later processing steps and protects the silicon wafer inthe source/drain areas. A thin blanket nitride barrier layer is thenformed over exposed surfaces. Next, a planarized blanket layer ofborophosphosilicate glass (BPSG) is formed, and a blanket nitride layeris formed over the BPSG layer. A patterned photoresist layer is formedover the blanket nitride layer which has an opening therein located overthe transistor sources. The nitride overlying the BPSG layer and theBPSG layer are etched using an anisotropic etch to keep sidewallsdefined by the nitride and BPSG formed as nearly vertical as possible.During this etch the BPSG is only partially etched to leave a portionover the source region.

Next, the photoresist layer is removed and a blanket conformal nitridelayer is formed and spacer etched to form nitride spacers along the BPSGsidewalls. After forming the spacers the BPSG remaining over the sourceregions is removed using a wet etch which is highly selective to nitriderelative to BPSG such that very little of the nitride barrier layer isremoved. As all exposed surfaces except for the BPSG to be removed arecovered by the thin nitride barrier layer, the nitride spacers, or thenitride layer overlying the BPSG, a highly selective wet etch can beused which has a high BPSG:nitride etch rate, rather than a dry etchwhich is much less selective between BPSG and nitride. A wet etch isavoided, for example to avoid etching the BPSG or damaging the tunneloxide which is exposed with conventional processing. Subsequently, thethin nitride barrier layer and the remaining gate oxide over the sourceregion is etched, and a conductive local interconnect layer is formedwithin the opening defined by the nitride to contact the source regions,for example using a damascene process. Finally, a contact andinterconnect to the source local interconnect is provided.

In accordance with another embodiment of the invention, a plurality oftransistor stacks each having an associated source and drain region, anitride capping layer, and nitride spacers formed along each stack isprovided. During the etch of the transistor stacks the gate oxide istypically not completely removed from the source and drain regions andremains until later processing steps and protects the silicon wafer inthe source/drain areas. A thin blanket nitride barrier layer is thenformed over exposed surfaces, and a BPSG layer is formed and planarized.While the BPSG is being planarized, it is possible to remove the thinnitride barrier layer from over the nitride capping layer, as well aspart of the nitride capping layer itself. Next, a patterned photoresistlayer is formed over the BPSG layer which leaves exposed a BPSG portionoverlying the source regions. A wet etch is used to remove the exposedBPSG down to the thin nitride barrier layer, then the nitride barrier isetched to expose the source regions. A source local interconnect isformed, for example using a damascene process, then wafer processingcontinues.

An in-process device formed in accordance with one embodiment of theinvention comprises at least two columns of transistors within a singlesector of a memory device, with each transistor having a source region.A dielectric layer having an opening therein defined by first and seconddielectric sidewalls is formed over the transistors, with one sidewalloverlying each column of transistors. The device further comprises:first and second dielectric spacers, wherein each of the spacers coversone sidewall of the dielectric layer; and a conductive line partiallyformed between the two columns of transistors and partially formed inthe opening in the dielectric layer between the first and seconddielectric sidewalls, wherein the spacers separate the conductive linefrom physical contact with the dielectric layer, and wherein theconductive line electrically couples each source region of eachtransistor in each of the two columns of transistors.

Use of this process allows for a more easily controlled exposure of thesource regions using a wet etch while protecting the gate oxide andother features from the etch. Thus the nitride spacers along thetransistor stacks and along the BPSG layer can be formed to be very thinand the distance between the stacks themselves can be formed to be verynarrow because of the controllable wet etch which is used to expose thesource region and the thin nitride barrier layer used to protect variousfeatures from the wet etch.

Additional advantages will become apparent to those skilled in the artfrom the following detailed description read in conjunction with theappended claims and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section depicting an arrangement of transistors, digitlines, and a source diffusion region formed as part of a conventionaldevice;

FIG. 2 is a cross section depicting an arrangement of transistors, digitlines, and a source local interconnect formed as part of a conventionaldevice;

FIGS. 3-12 are cross sections depicting a first inventive embodiment ofa method to form a source local interconnect; and

FIGS. 13-16 are cross sections depicting a second inventive embodimentof a method to form a source local interconnect.

It should be emphasized that the drawings herein may not be to exactscale and are schematic representations. The drawings are not intendedto portray the specific parameters, materials, particular uses, or thestructural details of the invention, which can be determined by one ofskill in the art by examination of the information herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of an inventive method for providing a flash memorydevice comprising a source local interconnect is depicted in FIGS. 3-12.The structure of FIG. 3, or a similar structure, is formed to comprisethe following: a semiconductor wafer 10, implanted transistor source 12and drain 14 diffusion regions, gate oxide 16, floating gates 18,capacitor dielectric 20, control gates 22, and a capping layer 24, forexample comprising silicon nitride (Si₃N₄). While four transistor stackscomprising layers 16-24 are depicted, it is conventional that atransistor array comprising several million transistors will be locatedover the surface of wafer 10.

The source regions 12 can comprise an arsenic-doped or phosphorous-dopedwell implanted in the wafer to an implant level of between about 1E13 toabout 1E15 atoms/cm². This is different from conventional flash deviceswhich have a source implant level of greater than 1E15 up to about 1E16atoms/cm². The lighter doping concentration of the inventive sourceregion allows the distance between source and drain regions to bedecreased. This decrease in spacing between source and drain regionsallowed by this embodiment of the present invention results, in part,from the reduction of the number of implanted atoms diffusing away fromthe high concentration regions of conventional source regions into thechannel region below the transistor stack. The remainder of the FIG. 3structure can be manufactured by one of ordinary skill in the art fromthe information herein for a flash device.

After forming the FIG. 3 structure, a blanket spacer layer 40, forexample a layer of silicon nitride, is formed over exposed surfaces ofthe wafer assembly as depicted in FIG. 4. A Si₃N₄ layer between about500 angstroms (Å) and about 1,000 Å thick would be sufficient. Such alayer can be formed by various chemical vapor deposition (CVD)processes, such as by introducing dichlorosilane gas (DCS, SiCl₂H₂) at aflow rate of about 90 standard cm³/minute (sccm) into a CVD depositionchamber along with about 270 sccm ammonia (NH₃) at about 600° C. forbetween about 30 minutes and about 90 minutes. After forming blanketlayer 40, it is etched using an anisotropic spacer etch to form nitridespacers 48 as depicted in FIG. 5. A sufficient spacer etch uses an argonplasma comprising argon at a flow rate of about 20 sccm, carbontetrafluoride (CF₄) at a flow rate of about 90 sccm, a radio frequency(RF) power of about 350 watts, a pressure of about 30 millitorr (mT) atemperature of about 20° C., and an etch time of between about 30 toabout 60 seconds. The spacers 48 are located over the gate oxide 16, andthe gate oxide remains exposed after formation of spacers 48.

After forming nitride spacers 48, a thin blanket etch-resistant layer50, such as a layer of silicon nitride between about 50 Å and about 100Å thick, is formed according to techniques known in the art. Layer 50covers all exposed features, but in particular covers the exposed gateoxide 16. Subsequently, a blanket planarized dielectric layer such asborophosphosilicate glass (BPSG) 52 is formed over the wafer surface.The wafers can be processed at between about 350° C. and about 400° C.in a chemical vapor deposition (CVD) furnace in an environmentcomprising silane (SiH₄), oxygen, phosphine (PH₃), and diborane (B₂H₆)for a target BPSG thickness of between about 2,000 Å and about 20,000 Å.The BPSG layer can then be planarized using a reflow process, forexample by processing the wafers at a temperature of about 900° C. forabout 25 seconds, then processed with an abrasive planarizationtechnique such as chemical mechanical planarization (CMP) to ensure asufficiently planar surface.

Subsequent to forming BPSG 52, a protective layer 54, for example anSi₃N₄ layer is formed over the surface of the BPSG layer 52. A nitridelayer having a target thickness of between about 200 Å and about 500 Åcan be formed by introducing 90 sccm DCS and 270 sccm NH₃ into a lowpressure chemical vapor deposition (LPCVD) furnace at a temperature ofbetween about 550° C. and about 650° C. for between about 30 minutes andabout 60 minutes.

A patterned photoresist layer 56 is formed over the surface of thenitride 54 such that an opening 58 in the photoresist 56 is above alocation overlying the source region 12 as depicted in FIG. 5.

After forming the FIG. 5 structure, an opening is etched in theprotective layer 54, then the BPSG 52 is etched such that a portion 60of the dielectric 52 remains over the source region 12 as depicted inFIG. 6. The etch of protective layer 54 and BPSG 52 can be performedusing a single etch, but it is preferably etched using two differentetch chemistries. For example, a nitride etch can comprise about 20 sccmargon, about 90 sccm CF₄, an RF power of about 350 watts, a pressure ofabout 30 mT, a temperature of about 20° C., and a duration of about20-40 seconds, and the BPSG etch can comprise about 70 sccm CHF₃, about20 sccm CH₂F₂, and about 50 sccm argon, for a duration of about twominutes. Regardless of whether the nitride and BPSG are etched using thesame etch or two different etches, the etch or etches are selected toremove the protective layer and the BPSG layer such that vertical ornear vertical sidewalls 62 are formed in the BPSG layer 52 as depicted.As shown in FIG. 6, this etch is timed to ensure that a portion of thedielectric 60 remains to cover the source region 12. In particular, thetop of layer 60 should be recessed below the top of capping layer 24between about 10% and about 50% of the thickness of capping layer 24,and should preferably be recessed between about 25% and about 50% of thethickness of capping layer 24.

After forming sidewalls 62 in dielectric layers 52 and 54 thephotoresist layer 56 is removed and a blanket conformal spacer layer 64is formed, for example a layer of silicon nitride, as depicted in FIG.6. This layer can be formed using a process similar to that describedabove to form layer 54, having a target thickness of between about 50 Åand about 300 Å. After forming blanket spacer layer 64, an anisotropicspacer etch is performed to form spacers 70 over the sidewalls 62 ofdielectric 52 and 54 as depicted in FIG. 7.

Subsequently, a wet etch is performed to remove the portion ofdielectric 60 covering source regions 12. A wet etch such ashydrofluoric acid (HF) diluted to about 25:1 water:HF for between aboutfive minutes and about 10 minutes is selected because a wet etch, ingeneral, provides for much higher BPSG etch rate relative to the nitridecapping layer 24, protective layer 54, etch-resistant layer 50, andspacers 48, 70. Layers 24, 54, 50, 48, and 70 protect the BPSG layerwhich is to remain, and allow the wet etch to completely removedielectric portion 60 to expose the source region 12. Layer 50 inparticular protects the portion of gate oxide 16 underlying spacers 48which would be exposed without layer 50, and prevents erosion of thegate oxide 16 from under spacers 48. The wet etch described removes BPSGselective to nitride, and thus the source region, and more particularlythe silicon wafer 10 into which the source region 12 is formed, is notdamaged by an over etch once layer 60 has been completely removed as itis protected by layer 50. After etching the BPSG and stopping on nitrideprotective layer 50, layers 50 and 16 which cover source region 12 areetched using an anisotropic dry etch. An etch which removes nitride andoxide selective to the silicon wafer includes CHF₃, CH₂F₂, and argonplasma gas. After etching layers 60, 50, and 16 over the source region12 of FIG. 7, the structure of FIG. 8 remains.

Next, a blanket conductive local interconnect layer is formed, forexample from polysilicon 90, to result in the structure of FIG. 9. Alayer of conductively doped polysilicon between about 500 Å and about2,000 Å may be formed by introducing silane gas (SiH₄) as a siliconsource into the chamber at a flow rate of between about 400 sccm andabout 600 sccm along with phosphine (PH₃) at a flow rate of betweenabout 5 sccm and about 15 sccm at a temperature of between about 500° C.and about 600° C. for a duration of between about four hours and about16 hours. Using this process the preferred material is formed at a rateof between about 10 Å/min to about 20 Å/min. While polysilicon ispreferred and is used in the description below, other materials such astungsten may be used. The description below for polysilicon can bemodified easily by one of ordinary skill in the art for the specificmaterial used.

The interconnect layer 90 is planarized, for example using an abrasiveplanarization technique such as CMP, to result in the damasceneplanarized polysilicon line 100 of FIG. 10. At this point the conductiveline electrically connects together the source regions for all thetransistors along a column of transistors. In this embodiment, thesources for each transistor are connected using the source LI and areotherwise separated by field oxide or shallow trench isolation (STI)oxide. In certain designs of flash devices, the local interconnect willelectrically connect the source regions for all the transistors alongtwo adjacent columns of transistors.

After electrically coupling all the sources within a column (or twocolumns) of transistors with polysilicon line 100, multiple conductivelines can be connected to electrically couple all source regions withina sector. This can be accomplished by forming a patterned dielectriclayer 110 having an opening which exposes polysilicon line 100 at leastat one location as depicted in FIG. 11, or at multiple locations toreduce electrical resistance through a single plug embodiment. A blanketconductive layer 112, for example tungsten, is formed to fill theopening in layer 110. Layer 110 is then planarized to form a pluralityof conductive plugs 120 in layer 110, one of which is depicted in FIG.12. At least one plug 112 contacts each conductive line 100 whichcouples a plurality of source regions in a column of transistors. Next,a conductive line 122, for example aluminum, is patterned to contactplugs 120 across multiple columns of transistors within a sector toelectrically couple the polysilicon lines 100 across multiple columns oftransistors, and thus electrically couple each source line withinmultiple columns of transistors of a sector.

A second embodiment of the inventive method is depicted in FIGS. 13-16.FIG. 13 depicts the following device structures: a semiconductor wafer10, implanted transistor source 12 and drain 14 diffusion regions, gateoxide 16, a floating gate 18, capacitor dielectric 20, a control gate22, and a capping layer 24, for example comprising silicon nitride(Si₃N₄). The source regions 12 can comprise an arsenic-doped orphosphorous-doped well implanted in the wafer to an implant dose ofbetween about 1E13 to about 1E15 atoms/cm². As stated in reference tothe prior embodiment, this is different from conventional flash deviceswhich have a source implant level of greater than 1E15 up to about 1E16atoms/cm². The lighter implant dose of the inventive source regionallows the distance between flash cell source and drain to be decreased.This decrease in spacing between the source and drain allowed by thisembodiment of the present invention results, in part, from the reductionof the number of implanted atoms diffusing away from the highconcentration regions of conventional source regions into the channelregion below the transistor stack. FIG. 13 further depicts dielectricspacers 48 and a thin (50 Å to 100 Å) nitride layer 50, each of whichcan be manufactured according to the prior embodiment, and the remainderof each transistor, specifically structures 10 and 14-24 can be obtainedor manufactured by one of ordinary skill in the art.

After forming structures 10-50, a dielectric layer 130, for example aBPSG layer, is formed then planarized using an abrasive planarizationtechnique such as CMP and stopping on the capping layer. Whiledielectric layer 130 is being planarized, it is possible to remove thinnitride layer 50 from over the nitride capping layers 24 as depicted, aswell as part of the nitride capping layer. Subsequently a patternedphotoresist layer 132 is provided which comprises an opening 134 locatedover the source region 12. An etch is performed to remove the exposeddielectric located over the source region 12 with a wet etch which onlyminimally etches capping layer 24 and nitride layer 50, and, if layer 50is removed, spacer layer 48. With silicon nitride layer 50, spacers 48,and capping layer 24, a wet etch such as hydrofluoric acid (HF) dilutedto about 25:1 water:HF for a duration of between about five minutes andabout 10 minutes is selected because a wet etch, in general, providesfor much higher BPSG etch rate relative to the nitride. Layers 132, 50,48, and 24 protect the portion of the BPSG layer which is to remain, thetransistor gate stack, and the source region 12. Thus, the BPSG over thesource region can be removed with a highly selective wet etch withoutdamaging the exposed gate oxide 16 under spacers 48.

After removing BPSG layer 130 and stopping on layer 50, layer 50 andgate oxide layer 16 are removed from over at least a portion of thetransistor source to expose the source region. Removal of theetch-resistant layer 50 formed from nitride and the gate (tunnel) oxidelayer 16 can be accomplished using an anisotropic dry etch. An exemplaryetch includes CF₄ at a flow rate of about 90 sccm, argon at a flow rateof about 20 sccm, an RF power of about 400 watts, a pressure of about 30mT for a duration of about 10 seconds to stop on the silicon wafer 10once layers 50 and 16 are removed. Subsequent to this etch the sourceregion 12 is exposed.

Next, a blanket conductive local interconnect layer is formed, forexample from polysilicon 140 to result in the structure of FIG. 14. Alayer of conductively doped polysilicon between about 500 Å and about2,000 Å may be formed by introducing silane gas (SiH₄) as a siliconsource into the chamber at a flow rate of between about 400 sccm andabout 600 sccm along with phosphine (PH₃) at a flow rate of betweenabout 5 sccm and about 15 sccm at a temperature of between about 500° C.and about 600° C. for a duration of between about four hours and about16 hours. Using this process the preferred material is formed at a rateof between about 10 Å/min to about 20 Å/min.

The polysilicon layer 140 (or other material used, for example tungsten)is planarized, for example using an abrasive planarization techniquesuch as CMP, to result in the planarized polysilicon line 150 of FIG.15. Subsequently, a patterned dielectric layer 152, for example BPSG, isformed, and a blanket conductive layer 154, for example tungsten, isformed to fill the opening in layer 152 as depicted. Layer 154 is thenplanarized to form a plurality of conductive plugs 160 in layer 152, oneof which is depicted in FIG. 16. At least one plug 160 contacts eachconductive line 150 which couples a plurality of source regions in acolumn of transistors. Next, a conductive line 162, for examplealuminum, is patterned to contact plugs 150 across multiple columns oftransistors, and thus electrically couple each source line withinmultiple columns of transistors of a sector.

A semiconductor device embodying the invention or manufactured using theinventive method has various uses in many electronic devices. Forexample an inventive device may be attached along with other devices toa printed circuit board, for example to a computer motherboard or as apart of a memory module used in a personal computer, a minicomputer, ora mainframe. The inventive device could further be useful in otherelectronic devices related to telecommunications, the automobileindustry, semiconductor test and manufacturing equipment, consumerelectronics, or virtually any piece of consumer or industrial electronicequipment.

While this invention has been described with reference to illustrativeembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the illustrative embodiments, as well asadditional embodiments of the invention, will be apparent to personsskilled in the art upon reference to this description. It is furtherapparent to those of ordinary skill in the art that there are otherdevice structures which have been omitted for simplicity of explanationof the invention. For example, a thin titanium layer may be formed priorto forming polysilicon layers 90 and 140 to enhance conductivity andadhesion between silicon wafer 10 and conductive lines 100 and 150. Itis therefore contemplated that the appended claims will cover any suchmodifications or embodiments as fall within the true scope of theinvention.

1. A flash memory device, comprising: a semiconductor wafer substrateassembly comprising at least a region of a semiconductor wafer; at leastfirst and second transistor columns overlying the semiconductor waferregion within a single sector of the flash memory device, wherein thefirst transistor column comprises at least a first transistor and thesecond transistor column comprises at least a second transistor and eachof the at least first and second transistors comprises: a transistorfloating gate; a transistor control gate overlying the transistorfloating gate; a dielectric capping layer having an upper surface; firstand second vertically oriented sidewalls at least partially formed by aportion of the dielectric capping layer, the transistor floating gate,and the transistor control gate; and a spacer formed along andcontacting the first vertically oriented sidewall and a spacer formedalong and contacting the second vertically oriented sidewall; an etchstop layer overlying the upper surface of the dielectric capping layerof each of the first and second transistors and which contacts thespacer formed along the first vertically oriented sidewall; a planarizeddielectric layer having a first vertically oriented sidewall whichoverlies the first transistor and a second vertically oriented sidewallwhich overlies the second transistor; a spacer formed along andcontacting the first vertically oriented sidewall of the dielectriclayer and a spacer formed along and contacting the second verticallyoriented sidewall of the dielectric layer; and a source localinterconnect interposed between the first and second transistors whichcontacts each spacer formed along the second vertically orientedsidewall of each of the first and second transistors and the spacersformed along the first and second vertically oriented sidewalls of thedielectric layer.
 2. The flash memory device of claim 1 furthercomprising the source local interconnect contacting the etch stop layer.3. The flash memory device of claim 1 wherein the dielectric layer is afirst dielectric layer and the flash memory device further comprises asecond dielectric layer formed over the first dielectric layer, whereinthe spacers formed along and contacting the first and second verticallyoriented sidewall of the first dielectric layer each contact the seconddielectric layer.
 4. The flash memory device of claim 3, wherein: eachspacer formed along and contacting the vertically oriented sidewalls ofthe first and second transistors comprises at least one silicon nitridelayer; the first dielectric layer comprises at least one silicon dioxidelayer; the second dielectric layer comprises at least one siliconnitride layer; and the etch stop layer comprises at least one siliconnitride layer.
 5. The flash memory device of claim 1 further comprisinga source diffusion region within the semiconductor wafer region at alocation between the first and second transistors, wherein the sourcelocal interconnect is electrically coupled with the source diffusionregion.
 6. The flash memory device of claim 5 wherein the sourcediffusion region is common to only the first and second transistorcolumns.
 7. The flash memory device of claim 1 wherein: the source localinterconnect comprises at least one polysilicon layer; and the flashmemory device further comprises a metal layer contacting the polysiliconsource local interconnect.
 8. The flash memory device of claim 1 furthercomprising a cross section across the first and second transistors andthe source local interconnect wherein the etch stop layer does notcontact the spacer formed along the second vertically oriented sidewall.9. The flash memory device of claim 8 wherein, at the cross section, theetch stop layer is not interposed between the first and secondtransistors.
 10. The flash memory device of claim 1 wherein the spacersformed along the first and second sidewalls of the dielectric layeroverlie and contact the etch stop layer.
 11. A flash memory devicecomprising, in cross section: a semiconductor wafer substrate assemblycomprising at least a region of a semiconductor wafer; at least first,second, third, and fourth transistor columns overlying the semiconductorwafer region within a single sector of the flash memory device, whereinthe cross section each transistor column comprises a transistor and eachtransistor comprises: a transistor floating gate; a transistor controlgate overlying the transistor floating gate; a dielectric capping layerhaving an upper surface; first and second vertically oriented sidewallsat least partially formed by a portion of the dielectric capping layer,the transistor floating gate, and the transistor control gate; and aspacer formed along and contacting the first vertically orientedsidewall and a spacer formed along and contacting the second verticallyoriented sidewall; an etch stop layer which contacts the spacer formedalong the first sidewall of the transistors of the first, second, third,and fourth transistor columns, and which contacts the spacer formedalong the second sidewall of the transistors of the first and fourthtransistor columns, but which does not contact the spacer formed alongthe second sidewall of the transistors of the second and thirdtransistor columns; a source local interconnect which contacts thespacer formed along the second sidewall of the transistors of the secondand third transistor columns and is interposed between the transistorsof the second and third transistor columns; a first dielectric layerhaving a first portion interposed between the transistors of the firstand second transistor columns and a second portion interposed betweenthe transistors of the third and fourth transistor columns; and a seconddielectric layer overlying and contacting the first, second, third, andfourth transistor columns and overlying and contacting the first andsecond portions of the first dielectric layer.
 12. The flash memorydevice of claim 11 wherein: each spacer formed along and contacting thevertically oriented sidewalls of the transistors of the first, second,third, and fourth transistor columns comprises at least one siliconnitride layer; the first dielectric layer comprises at least one silicondioxide layer; the second dielectric layer comprises at least onesilicon dioxide layer; and the etch stop layer comprises at least onesilicon nitride layer.
 13. The flash memory device of claim 11 whereinthe source local interconnect is free from contact with the source localinterconnect.
 14. The flash memory device of claim 11 furthercomprising: a metal plug formed within an opening in the seconddielectric layer which contacts the source local interconnect; and ametal interconnect formed over the second dielectric layer and whichcontacts the metal plug.
 15. The flash memory device of claim 14 furthercomprising a source diffusion region in the semiconductor wafer region,wherein the source local interconnect is electrically coupled with thesource diffusion region.
 16. An electronic device comprising a flashmemory device, wherein the flash memory device comprises: asemiconductor wafer substrate assembly comprising at least a region of asemiconductor wafer; at least first and second transistor columnsoverlying the semiconductor wafer region within a single sector of theflash memory device, wherein the first transistor column comprises atleast a first transistor and the second transistor column comprises atleast a second transistor and each of the at least first and secondtransistors comprises: a transistor floating gate; a transistor controlgate overlying the transistor floating gate; a dielectric capping layerhaving an upper surface; first and second vertically oriented sidewallsat least partially formed by a portion of the dielectric capping layerand the transistor control gate; and a spacer formed along andcontacting the first vertically oriented sidewall and a spacer formedalong and contacting the second vertically oriented sidewall; an etchstop layer overlying the upper surface of the dielectric capping layerof each of the first and second transistors and which contacts thespacer formed along the first vertically oriented sidewall; a planarizeddielectric. layer having a first vertically oriented sidewall whichoverlies the first transistor and a second vertically oriented sidewallwhich overlies the second transistor; a spacer formed along andcontacting the first vertically oriented sidewall of the dielectriclayer and a spacer formed along and contacting the second verticallyoriented sidewall of the dielectric layer; and a source localinterconnect interposed between the first and second transistors whichcontacts each spacer formed along the second vertically orientedsidewall of each of the first and second transistors and the spacersformed along the first and second vertically oriented sidewalls of thedielectric layer.
 17. The electronic device of claim 16 wherein thesemiconductor memory device further comprises the source localinterconnect contacting the etch stop layer.
 18. A flash memory device,comprising: a semiconductor wafer substrate assembly comprising at leasta region of a semiconductor wafer; at least first and second transistorcolumns overlying the semiconductor wafer region within a single sectorof the flash memory device, wherein the first transistor columncomprises at least a first transistor and the second transistor columncomprises at least a second transistor and each of the at least firstand second transistors comprises: a transistor floating gate; atransistor control gate overlying the transistor floating gate; adielectric capping layer having an upper surface; first and secondvertically oriented sidewalls at least partially formed by a portion ofthe dielectric capping layer, the transistor floating gate, and thetransistor control gate; and a spacer formed along and contacting thefirst vertically oriented sidewall and a spacer formed along andcontacting the second vertically oriented sidewall; a source localinterconnect interposed between the first and second transistors whichcontacts each spacer formed along the second vertically orientedsidewall of each of the first and second transistors and the spacersformed along the first and second vertically oriented sidewalls of thedielectric layer; and a transistor source within the semiconductor wafercomprising a well region implanted with dopants to a concentration ofbetween about 1E13 to less than about 1E15 atoms/cm², wherein the sourcelocal interconnect overlies and electrically contacts the transistorsource.
 19. The flash memory device of claim 18 further comprising: anetch stop layer overlying the upper surface of the dielectric cappinglayer of each of the first and second transistors and which contacts thespacer formed along the first vertically oriented sidewall; a planarizeddielectric layer having a first vertically oriented sidewall whichoverlies the first transistor and a second vertically oriented sidewallwhich overlies the second transistor; and a spacer formed along andcontacting the first vertically oriented sidewall of the dielectriclayer and a spacer formed along and contacting the second verticallyoriented sidewall of the dielectric layer.